In the manufacture of certain molded products, it is necessary that particular pathways, chambers, or other openings be created within the molded products in order for them to accomplish their intended service application. For example, various plastic automotive parts often require channels or openings therein through which various fluids flow. Oftentimes, these openings cannot be made using permanent, reusable molds and the like, and the only manner by which to produce these openings is to mold the product around a one time only core complementing the configuration of the intended openings, and then, to destroy or disintegrate the core, thereby leaving the openings available for their intended purpose.
Such cores are commonly used in the foundry and investment casting industries and must be made of materials which are not only dimensionally agile enough to be formed into discrete, complex shapes or configurations so as to complement the voids or openings to be created in the molded product, but also must be mechanically and chemically strong enough to withstand the molding process for the application they are intended, yet mechanically or chemically weak enough to be easily destroyed and disintegrated upon completion of the molding process.
Over the years, various materials and procedures have been employed in the forming and removal of such cores. In the foundry industry, various low melt metals, such as tin, bismuth and other low melt alloys, have been used to form the complementary, complex shape of the desired opening. This metal core was then positioned in the mold and the material from the finished product, e.g., a high temperature metal, was pored or injected in to the mold about the core. Once the material solidified or was cured, the entire product was heated to a temperature above the melting point of the metal core, and the melted material was removed by slowly pouring it out of the resultant product.
Similarly, foundry sand compositions wherein the sand particles have been bound together by particular binder materials, such as phenolic resins, have been used to form foundry cores. After forming the cores, they were then positioned in the mold and subjected to the materials (e.g., metals) of the finished product during the molding process. Typically, the binder materials in the cores were designed to degrade or decompose upon the application of the high temperatures required to cure the resultant product, thereby significantly weakening the remaining sand core. Thus, once the molded product was solidified or cured, the core sand was easily removed by vibrating the product to disintegrate the core, and/or blowing the remaining sand or other particles out of the resultant shell.
However, it will be appreciated that these methods depend significantly upon the application of heat or, at least, upon the use of extremely high temperatures to obtain the intended result. While these procedures may be suitable for the foundry industry, they are, oftentimes, not suitable for the investment casting industry or other industries where non-metal products such as those made of plastics, waxes, and polymeric materials cannot be subjected to these extreme temperatures.
Thus, other methods for the production and removal of cores have been developed. For example, U.S. Pat. No. 5,262,100 relates to a method for the removal of a sand core from a molded product by using a heat-cured, water soluble binder such as silicate salt (e.g., sodium silicate or potassium silicate), plastic firebrick, gelatin, or resinate salt. That is, after the resultant, flinised product has been molded, the core is exposed to water so as to rapidly disintegrate and wash away the core.
Such water soluble cores offer sign ficant advantages over certain other types of cores in that they often require less tooling and can be made with less costly materials. The ability to collect and recover the remaining sand and/or aggregate particles for reuse in also seen as advantageous. Moreover, these cores operate at relatively low temperatures (typically in the range of from about 150.degree. F. to about 250.degree. F.) compared to non-water soluble, foundry cores (where temperatures may reach 1300.degree. F. or higher), thereby requiring less heat energ) to use them as compared to certain non-water soluble, foundry cores.
Unfortunately, the water soluble cores described hereinabove suffer from the disadvantage in that the water soluble binders employed, e.g., sodium silicate, are significantly hygroscopic. Thus, it is often difficult to remove all of the water from the core, requiring additional time (2-5 minutes) and energy in the production thereof, and it is even more difficult to keep water away from the core. Thus, as soon as the core is produced, it must be placed in a container so prevent water from contacting it. Even then, due to the hygroscopic nature of the binder materials, the shelf life of each core is relatively short, and far less than for other cores.
Moreover, these binders can be very tacky if they are not used in just the right amounts for the production of the core. Thus, having the resultant core stick to the manufacturing dye remains a potential problem.
Thus, the need exists for a core comprising a water soluble binder which is not as readily hygroscopic of those binders des;cribed hereinabove, and has better release properties than other water soluble binders.